1. Field of the Invention
The present invention relates to a composition of coating solution using water as a main solvent, which is employed for applying a coating film which is moisture proof to a solid preparation.
2. Description of the Prior Art
More particularly, the invention relates to a coating composition which yields a coating having good luster and smooth taste as well as being moisture proof, which has a masking effect preventing the active ingredient in the preparation from being released in the mouth before swallowing, and which has a definite and suitable delay of dissolution ensuring rapid release of the content after swallowing.
To the tablet, pill and granule is usually applied a coating by using various kinds of high-molecular compounds as coating material, in order to prevent degeneration or decomposition of the active ingredient due to hygroscopic or other cause either in the process of manufacture or during the storage time until it is administered. As high-molecular compounds employed for this purpose are known shellac, cellulose acetate phthalate (CAP), methyl vinyl pyridine.methyl acrylate.methacrylic acid copolymer (MPM), ethyl cellulose (EC), polyvinyl acetal diethylaminoacetate (AEA) and the like.
In performing the coating with such high-molecular compounds as mentioned above, they are generally dissolved in an organic solvent with high volatility and then the resulting solution is used for spray-coating. In this case, the organic solvent is discharged into the air along with the exhaust air to become a source of air-polution, and a provision is therefore required to wash the exhaust air with water to trap the organic solvent. Furthermore, in order to keep a good working environment, a lot of expense is required for air-conditioning equipment, antiexplosion provision for electric appliances and others, and the cost of the solvent employed is by no means negligible.
Such problems seem to be solved by using water as a coating solvent, but they have still remained unsettled for various reasons. The first reason is the absence of water-soluble film bases which are highly moisture proof, and the second is that, when an aqueous coating solution is employed, the moisture penetrates into the preparation during the process of spraying.
There is already known a liquid coating composition which comprises blending stearic acid or the like for imparting moisture proof properties to a water-soluble film base having poor moisture resistance in itself, such as hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), an organic acid salt of AEA or the like. In this case, however, there is the disadvantage that the use of organic solvent becomes inevitable for dissolving stearic acid.
One of the most important requisites for the coated solid medicine orally administered is to have a masking property preventing the active ingredient having a pungent taste and unpleasant smell from being released out of the preparation into the mouth. Such a property of the coating film must be compatible with a property to rapidly release the content of the preparation after swallowing so as not to lower the bioavailability of medicine. Such a characteristic can be estimated in the dissolution test of the preparation by observing the delay of dissolution, which means a complete prevention to release the active ingredient for a definite time, and the subsequent rapid release. The delay of dissolution is usually sufficient if it is 1 to 5 minutes, and it is desirable that is be freely regulated by selecting the conditions in preparing the coating film.
In view of such a present situation, the present inventors have earnestly attempted to solve these problems and have succeeded in preparing an improved coating film which fully satisfies all of the above-mentioned problems.